Here is a real world analogy - a doorman on duty at a nightclub.
The technique we use here is the right hand KO punch, but in four different examples, each a manifestation of an element of the Godai.
Each scenario presented here is a real situation I have faced in my career.
There is NO THEORY here - each example is 100% REAL!
Earth
Standing on the door you are Earth, the mountain, the oak tree, immovable. You tell a customer he can't come in. You are strong and confident. Nobody is getting past you. You ARE the Door!
The customer gets angry and steps up to attack. From The Fence you land your KO punch to his jaw and knock him out. You have no need to be afraid or angry, you have no need to attack or defend. You simply apply the correct response for the situation at hand.
Fire
The alarm goes and you rush inside to see a full blown fight has erupted on the dance floor.
You move straight in and knock out each man who is fighting. If they are not trying to get away they are trying to get stuck in, so you neutralise them. One, two, three, you crack your KO punch to their jaw and they drop to the floor. You are Fire, an unstoppable force of nature.
Water
One of the other doormen goes to deal with a customer, to ask him to leave. Suddenly CRACK! The doorman goes down. This is no ordinary customer but a dangerous, trained, experienced fighter. As you move in he squares up to you. You are now in a fight with a skilled opponent.
You react, you defend and you counter. You nullify his attacking blows and set up your opportunity to land your KO, taking him out of the game.
Wind
A drunk customer is being rowdy and it is time to ask him to leave. You can't allow him to hurt another customer, yourself, or a member of your team, but you can't allow him to hurt himself either. Nor is it appropriate to go in with maximum force, maybe breaking his jaw or arm.
You do your best to avoid a violent solution. The drunk swings at you. You parry his first swing, and maybe his second. But when he swings a third time you use the Captain's Log to parry down his attack and then land your KO. You gave him every chance.
To take this analogy further, rather than the punch, from the Log use ikkyo to take him to the floor and restrain him. Then call another doorman to take his other arm and walk him out together so nobody needs to get hurt.
So you see the KO punch, which theoretically is a Fire technique, can be used as a technique by any of the four elements you are manifesting, as the situation demands.
DO NOT restrict yourself to any element, art, or technique or you are destined to fail.
Sometimes it is appropraite to be Fire.
Sometimes you need to be Wind or Water.
Most times you just need to be Earth.